Plumbing
Sump pump and sewage ejector sizing field guide for plumbers
Pick the right pump, size it to the flow and the total dynamic head off the curve, build the basin and discharge the code wants, and prove it cycles and alarms before you leave.
Direct answer
A sewage ejector pump lifts sewage with solids up from below-grade fixtures to the gravity sewer when the drain sits below the sewer line, while a sump pump moves only clear groundwater out of a sump. Size both to the flow and the total dynamic head, and follow the adopted plumbing code, IPC or UPC.
Key takeaways
- A sewage ejector lifts raw sewage with solids from below-grade fixtures to the gravity sewer; a sump pump moves only clear groundwater and passes no solids.
- A sewage ejector receiving a water closet must pass a 2 in spherical solid, per IPC Section 712 and the equivalent UPC ejector section.
- Under the UPC, a single dwelling ejector passes a 1 1/2 in solid with a 2 in minimum discharge; other buildings need a 2 in ball and 3 in discharge.
- Size to total dynamic head (static lift plus friction head) and pick the pump where design GPM and TDH cross on the manufacturer's curve, not on horsepower.
- Sewage basins require a sealed gas-tight cover, a vent to atmosphere, a check valve closest to the pump, a downstream gate valve, and at least 6 in of float travel.
Pumping up when gravity will not do it
Plumbing wants to run downhill. When the fixture or the water sits below the line it has to reach, gravity quits and a pump takes over. That is the whole job here. A sump pump and a sewage ejector both lift liquid up to where it can drain by gravity again, but they handle two different liquids and you do not get to mix them up.
A sump pump moves clear water. Groundwater and stormwater collect in a sump pit, the float trips, and the pump pushes that water out to daylight, a storm line, or a drywell. No solids, no sewage, nothing that smells. A sewage ejector moves raw sewage with solids from a toilet, a shower, a laundry, or a floor drain that all sit below the building sewer. It passes the solids whole, lifts the waste into the gravity drain overhead, and the basin has to be sealed and vented because what is in it is sewer gas.
Get the wrong pump in the pit and you find out fast. A sump pump put on a sewage load clogs on the first wad of toilet paper, because it was never built to pass a solid. That single substitution is one of the most common callbacks in below-grade work, and it is the one that backs sewage up into a finished basement.
What is the difference between a sump pump, a sewage ejector, and a grinder pump?
A sump pump handles clear water, a sewage ejector handles raw sewage with solids, and a grinder pump shreds the solids into a slurry so it can push them a long way through small pipe. Those are three machines for three different problems, and the discharge they need is the fastest way to tell them apart.
The sewage ejector is the workhorse for a below-grade bathroom tied to a nearby gravity sewer or a septic tank. It is a high-volume, lower-pressure pump that spins an open impeller and passes solids whole. It does not grind. When the destination is a septic tank you want the ejector, not the grinder, because the septic system needs the solids intact to separate and settle. Grind them and the septic field pays for it.
The grinder is the answer when you have to push sewage a long distance or up a steep lift through a small-diameter force main, usually into a pressurized municipal sewer. It is a low-volume, high-pressure pump with cutting blades, commonly moving 35 to 70 gpm but over hundreds or thousands of feet. If the job is a single basement bath dropping into a gravity main twenty feet away, a grinder is the wrong tool and the wrong money. Match the pump to the destination and the distance, then size it.
| Pump | Liquid | How it handles solids | Typical use |
|---|---|---|---|
| Sump pump | Clear groundwater, stormwater | Passes none; clear water only | Foundation drainage, sump pit, never sewage |
| Sewage ejector | Raw sewage with solids | Passes solids whole, open impeller | Below-grade fixtures to a nearby gravity sewer or septic tank |
| Grinder pump | Raw sewage, ground to slurry | Cuts solids with blades | Long or high lift into a small pressurized force main |
Why a below-grade fixture forces a pump
Run a line off the building sewer and trace it back. Every fixture above that invert drains by gravity. Every fixture below it cannot, and that is the test for whether you need a pump at all. A basement bath, a below-grade laundry, a floor drain in a sub-basement mechanical room, an areaway drain that sits under the street sewer, all of them are below the gravity line and have to be lifted.
Decide gravity versus pumped before you frame anything. Shoot the invert of the building sewer where it leaves the foundation, then shoot the trap arm of the lowest fixture. If the fixture drains downhill to that invert with the slope the code wants, run it by gravity and skip the pump entirely. A pump you did not need is a lifetime of maintenance and a guaranteed failure point you built in for no reason. If the fixture sits at or below the invert, you are pumping, and now the question is sump or ejector.
The sump side of the same building is the foundation drainage. The footing drain or the under-slab drain tile gathers groundwater and routes it to a sump pit. That water has to leave too, and if the pit cannot drain to daylight by gravity, a sump pump empties it. Keep that water out of the sewer; in most jurisdictions you may not dump clear groundwater into the sanitary system, and the storm side or daylight is where it belongs. Confirm the discharge point with the AHJ before you pipe it.
How big a solid does a sewage ejector pass, and what discharge does it need?
A sewage ejector that receives the discharge of a water closet has to pass a 2 in spherical solid. That number drives the impeller, the inlet, and the discharge size, and it is written into the ejector provisions of the plumbing code, commonly Section 712 of the IPC and the equivalent ejector section of the UPC. Read it as a floor, not a target. The pump is rated for the largest ball it will pass, and that rating has to meet the requirement for what it serves.
The discharge size splits on the building type under the UPC, and people miss the split. For a single dwelling unit, the code commonly allows the pump to pass a 1 1/2 in solid with a discharge not smaller than 2 in. For anything other than a single dwelling, the pump has to pass a full 2 in solid and the discharge cannot be smaller than 3 in. So the residential basement bath and the commercial below-grade restroom are not the same spec, and an inspector on a commercial job will look for the 2 in ball rating and the 3 in discharge.
A grinder is the exception that proves the rule. Because it shreds the solids, it does not pass a 2 in ball and it does not need a 2 in or 3 in discharge. Grinder discharge is commonly 1 1/4 in minimum, because the whole point is to push a slurry through small high-pressure pipe. Confirm the exact figures against the adopted code edition and any local amendments before you cut pipe, because the discharge minimum is the one the inspector measures.
| Service | Solid the pump must pass | Minimum discharge |
|---|---|---|
| Sewage ejector, single dwelling | 1 1/2 in ball | 2 in |
| Sewage ejector, other than single dwelling | 2 in ball | 3 in |
| Pump receiving a water closet | 2 in solid handling | Per the above by building type |
| Grinder pump | Grinds, passes no large solid | Commonly 1 1/4 in |
How do you size the flow in GPM?
The flow side of the pump selection is the gallons per minute it has to move, and you get there two different ways depending on what the pump serves. A sump pump is sized to the water coming in. A sewage ejector is sized to the fixtures draining into it. Same units, different source for the number.
For a sump pump, the flow you size to is the peak inflow into the pit, the groundwater rate at its worst. The honest way to find it is to let the pit fill with the pump unplugged, measure how fast the level rises, and convert that to gpm at the pit's cross-section. The lazy way is to guess, and the guess is always low because nobody tests in a wet spring. Size the pump to beat the peak inflow with margin to spare, because the pit that keeps up in August is the pit that overflows in March.
For a sewage ejector, the flow comes from the fixture load draining into the basin. Total the drainage fixture units of the fixtures it serves, convert that to a peak discharge in gpm, and size the pump to clear it. A single basement bath is a small number and a 1/2 hp residential ejector usually covers it. A bank of commercial restrooms is a real load and gets a real calculation. See the DWV venting and pipe sizing guide for how drainage fixture units add up; the same fixture-unit total that sizes the drain is what sizes the pump that lifts it.
Whichever side you are on, the GPM is only half the selection. You pick the pump where its flow and its head cross on the curve, and the head is the part people shortchange.
Total dynamic head and reading the pump curve
Total dynamic head, TDH, is the total resistance the pump has to overcome to move the water, measured in feet of head. It is the static lift plus the friction in the discharge piping, and you cannot pick a pump without it. A pump rated for 50 gpm at 10 ft of head is not the same pump as 50 gpm at 30 ft, and the basin that pumps fine on the bench can fail in the building because the head was never figured.
Static head is the vertical distance from the pump-off water level in the basin up to the highest point of the discharge before it drops into the gravity drain. Measure it as a real elevation difference, not the height of the basin. Friction head is everything the water loses fighting its way through the pipe, the elbows, the check valve, and the fittings on the way up. You get it from a friction-loss chart at your design gpm, multiplied by the pipe length plus the equivalent length of every fitting. On a short residential run the friction is small and the lift dominates. On a long horizontal run it can outweigh the lift, which is why you cannot eyeball it.
Add the two, and that TDH is the head you carry to the manufacturer's pump curve. Find your design gpm on the bottom axis, run up to the curve, and read across to the head. If the curve sits at or above your required head at that flow, the pump makes it with margin. If you land below the curve, the pump cannot deliver your gpm against that head and the basin will back up. The curve governs the selection, not the horsepower on the label. A bigger motor on a flat curve still loses to the head.
Undersize the head and the pump runs long, overheats, and burns out early while the water rises behind it. Oversize it wildly and you get a pump that empties the pit in seconds and short cycles itself to death. The point is to land on the curve where the flow and the head you actually have meet, with a little room, not at either extreme.
TDH = Hstatic + HfrictionHstatic = elevdischarge high point − elevpump-off levelHfriction = (Lpipe + Lfittings) × f100 / 100- H static
- Static lift in feet, the vertical rise from the pump-off water level to the high point of the discharge
- H friction
- Friction head in feet, the loss through pipe, fittings, and the check valve at the design flow
- f100
- Friction loss in feet per 100 ft of pipe at the design gpm, read from a friction chart for the pipe size and material
- L fittings
- Equivalent length in feet that elbows, valves, and fittings add to the straight pipe length
The basin: sump pit versus sealed sewage basin
The pit is not an afterthought, it is part of the pump system, and the sump basin and the sewage basin are built to different rules. A sump basin can be a perforated or open pit because it is collecting groundwater you want it to gather. A sewage basin has to be a gas-tight, sealed unit with a removable gas-tight cover, because it is holding raw sewage and the sewer gas that comes off it. The code is explicit that the ejector pit is covered, gas-tight, and vented.
Size the basin for the drawdown, which is the volume between the pump-on and pump-off floats. That working volume sets the cycle. Too small a basin and the pump starts and stops constantly, which is the single most common cause of an early pump death. The manufacturer gives a minimum basin diameter and depth for their pump and float arrangement; use it. A common floor in the field is to keep enough drawdown that the pump runs a real cycle, not a blip, and to keep at least 6 in of travel between the on and off points so the floats are not tripping each other.
The sewage basin cover carries the floats, the discharge penetration, and the vent, and every penetration has to be sealed. The cover bolts down and seals to the basin so the only path for gas is the vent, not the cover seam and not around the discharge pipe. A cover that does not seal turns a finished basement into a sewer-gas problem, and the homeowner smells it long before anyone calls it a code violation.
Does a sewage ejector basin need a vent?
Yes. A sewage ejector basin has to be vented to atmosphere, and it is not optional. The basin is a sealed box full of sewage and sewer gas, and as the pump fills and empties it, the air inside has to go somewhere. Without a vent the pump fights a pressure swing it was never built to overcome, the floats behave erratically, and the gas finds its own way out, which means into the building. The plumbing code routes that vent the same way it routes any other vent, through the venting provisions of the code.
The vent off the basin ties into the building's vent system and carries to atmosphere the same way the rest of the DWV vents do. It cannot dead-end and it cannot just terminate under the cover. Size and connect it per the venting requirements of the adopted code, commonly Chapter 9 of the IPC or the venting chapter of the UPC, and confirm the connection rules with the AHJ. See the DWV venting and pipe sizing guide for how vents protect trap seals and how the vent network ties together; the ejector vent is part of that same system, not a separate animal.
A sump pit handling only clear groundwater is a different case and does not carry the same sewer-gas venting requirement, because there is no sewage and no gas to manage. The sealed, vented basin is specifically the sewage rule. Do not seal a sewage basin and skip the vent, and do not leave a sewage basin open thinking the vent makes the cover optional. It needs both: sealed cover and vent.
The check valve, the gate valve, and the union
On the discharge of a sewage pump or ejector you install a check valve and a gate valve, and the code requires both. The check valve stops the column of water and sewage in the riser from falling back into the pit every time the pump shuts off. The gate valve goes on the discharge side of the check valve so you can isolate the line and service the check valve or pull the pump without draining the whole riser back into the basin.
Order and position matter. The check valve sits closest to the pump, the gate valve sits downstream of the check valve, and a union goes in so the pump can come out without cutting pipe. Mount the check valve where the code and the manufacturer want it, commonly on a vertical or slightly inclined run above the basin, not buried flat at the bottom where solids settle on the flapper and hold it open. A check valve laid wrong is a check valve that does not check.
Skip the check valve and you build a short-cycling machine. The pump empties the riser, shuts off, the riser drains straight back into the pit, the float trips again, and the pump runs again on the same water it just moved. That is wasted runtime, wasted power, and a pump that wears out years early. The check valve is the cheapest part on the discharge and the one that does the most to keep the pump alive.
How do the float switches and the controls work?
The float switch is what tells the pump when to run. As the level rises, the float rises and closes the switch; as the level drops, the float drops and opens it. The travel between those two points is the drawdown, and where you set the floats decides whether the pump runs a healthy cycle or beats itself to death. Set the on point high enough to give a real volume to pump and the off point above the pump's intake so it never runs dry.
Two styles cover most work. A tethered float hangs on a cord and flips as the level swings; it suits a larger basin and is the common choice on sewage ejectors because it gives a wide on-to-off swing. A vertical float rides up and down a rod and suits a tight basin where a tethered float would snag on the wall or the pipe. In a small pit a tethered float that catches on the discharge is a classic stuck-float failure, so the vertical float earns its place there.
Above the working floats sits the high-water alarm, and on anything you care about it is not optional. It is a separate float set above the pump-on level that triggers an audible or remote alarm when the water rises past where the pump should have caught it. That alarm is the warning that the pump failed, the float stuck, or the inflow beat the pump, and it is the difference between a service call and a flooded basement. Wire it so it works when the pump's own circuit is dead, because the alarm that shares the failed pump's power is no alarm at all.
Duplex pumps and the alarm panel
On a critical sewage load you do not run one pump. You run two in a duplex arrangement with an alternating control, so a single pump failure does not take the system down and back sewage into the building. The alternator switches which pump leads on each cycle, which evens the wear so both pumps age together instead of one running every cycle while the other sits and seizes.
The duplex panel earns its keep two ways. It alternates the lead and lag pumps, and it brings the lag pump on automatically when the inflow beats the lead pump alone, so a peak that one pump cannot clear gets both. On top of that sits the high-water alarm, which fires when the water rises past both pumps' run points, telling you the system is losing the fight before the floor does.
Where the duplex is worth the money is anywhere a backup down for a day is unacceptable: an occupied commercial building, a healthcare or food-service space, any below-grade sewage that cannot wait for a Saturday service call. A single residential basement bath usually runs simplex with a good alarm. A building full of people on a below-grade sewer runs duplex, because the question is not whether a pump fails but whether you are standing in the result when it does.
Discharge piping and the force main
The discharge piping is sized to the pump and the discharge minimum the code sets, not to whatever fitting is on the truck. For a residential ejector that is commonly 2 in, for a commercial ejector 3 in, and for a grinder commonly 1 1/4 in, matched to keep the solids moving without settling. Run the riser up, through the check valve and gate valve, and tie into the gravity drain overhead where the waste can run downhill the rest of the way.
A force main behaves differently from a gravity drain and you pipe it differently. Because the pump is pushing under pressure, the force main does not need slope the way a gravity line does, and it should not be trapped. A trap or a low sag in a pressurized line holds solids and air and chokes the flow. Keep it running clean to the point where it discharges into gravity, and on a grinder line hold the velocity up, commonly around 2 ft per second, so the slurry never settles and clogs the small pipe.
Where the force main hands off to gravity, do it right. Tie in so the pressurized flow discharges into the gravity drain or the manhole without shooting back up the vent or splashing out, commonly entering near the top of the receiving pipe rather than the bottom. Confirm the tie-in detail and the discharge point against the adopted code and the AHJ, because the connection from pumped to gravity is where the design either works or backs up.
The electrical and the battery backup
A sump or sewage pump runs off a dedicated circuit, and on a 120 V residential pump that commonly means its own receptacle on its own circuit, not shared with the laundry or the freezer that trips it offline. Whether GFCI protection is required depends on the location and the adopted electrical code, so confirm it against the NEC edition the jurisdiction has adopted rather than assuming. The pump that nuisance-trips a shared GFCI in the middle of a storm is the pump that was wired as an afterthought.
The thing that kills a sump pump is not usually the pump, it is the power. The storm that floods the basement is the same storm that drops the grid, so the pump quits exactly when the water is highest. That is why a sump on a finished basement gets a backup: a battery backup pump that runs off a deep-cycle battery, or a water-powered backup that runs off the municipal supply pressure and needs no electricity at all. Each has a cost. The battery runs dry after hours and needs maintenance; the water-powered unit wastes potable water and needs adequate street pressure. Pick for the site, but pick something.
Wire the high-water alarm so it survives the pump's failure mode. An alarm on the same dead circuit as the pump tells you nothing during a power loss. A battery-backed or independently powered alarm tells you the main pump is down while there is still time to do something about it.
Installing it and testing it before you leave
Set the basin plumb and on a stable base so it cannot float or shift, make the discharge and vent connections, seal every penetration on a sewage cover, and set the floats to give a real drawdown with clearance from the wall and the pipe. None of that is the hard part. The hard part is that crews call it done when the pump is in the hole, and the system is not done until it has been filled and cycled.
Test it on water. Fill the basin and watch the pump start at the on float, run a full cycle, and shut off at the off float without short cycling. Confirm the check valve holds by listening for the riser draining back after shutoff; if it refills the pit, the check valve is wrong or installed wrong. Lift the high-water alarm float by hand and confirm it actually alarms. On a duplex, force the lead pump off and confirm the lag pump picks up and the alternator hands off on the next cycle.
Then watch a few cycles, not one. A single cycle can look fine while a float that is set too tight or a check valve that seeps shows up only on the third or fourth run. Time the cycle, confirm it is not starting every thirty seconds, and confirm the pump-off level keeps the intake submerged. The test that finds the problem is the one you run before the cover is sealed and the drywall is up, not the callback six weeks later.
Why does my pump short cycle?
A pump short cycles when it starts and stops every few seconds or minutes instead of running a real cycle, and it is hard on the motor because the start is the moment of highest stress. Run the short list in order, because the cause is almost always one of four things and they rank by how often they bite.
A failed or missing check valve is first. Without it the riser drains back into the pit the instant the pump shuts off, the float trips again, and the pump runs on the same water it just moved. A basin that is too small is second; with little drawdown the level swings through the on and off points almost instantly. A float set too tight or stuck is third, where the on and off points are too close together or the float catches on the wall or the discharge. And an oversized pump is fourth, emptying the pit faster than it can refill so the float drops out the moment it pumps down.
The fixes follow the causes. Replace or reposition the check valve, increase the basin or the drawdown, reset the floats to give at least 6 in between the on and off points, or right-size the pump to the actual flow. A pump that cycles every thirty seconds will not last a year, and replacing it without fixing the cause just buys you another short-lived pump.
Commercial cases: elevator sumps, oil, and below-grade pump rooms
An elevator pit sump is its own problem because of what ends up in it. Groundwater collects in the pit, but so does hydraulic oil from the elevator and machine room, and you may not pump oily water into the sanitary or the storm system. The common requirement is an oil-detecting pump or an oil-minder control that will not discharge when oil is present, often paired with an oil interceptor or separator, so the pump moves water and holds the oil back. The exact requirement is set by the plumbing code, the elevator code, and the AHJ together, so confirm it for the project rather than treating it like an ordinary sump.
A below-grade pump room or a deep mechanical space in a commercial building concentrates the stakes. The sewage from the fixtures and the floor drains down there is lifting to a sewer overhead, and a failure floods equipment, not just a finished basement. These are the rooms that get duplex pumps, a real high-water alarm tied to the building management system, and a maintenance plan, because the cost of a failure is measured in downtime, not drywall.
Data centers and other critical below-grade rooms push it further. Anywhere the water rises into live equipment, the pump system is part of the building's resilience, not a plumbing detail. Duplex pumps, monitored alarms, backup power on the controls, and a tested response are the baseline, and the design coordinates with the mechanical and the electrical so a wet floor never reaches what cannot get wet. Size and redundancy follow the consequence of failure, and in those rooms the consequence is high.
What the owner has to maintain
A pump system is not install-and-forget, and the owner inherits a maintenance load whether anyone tells them or not. The float, the check valve, the basin, and the alarm all need periodic attention, and the failure that floods a basement is usually a maintenance item nobody touched, not a pump that wore out.
Tell the owner what to check and how often. Lift the alarm float and confirm it alarms, on a schedule, because the alarm is the one part you cannot tell is dead until you need it. Pour water in and confirm the pump cycles and shuts off cleanly. On a sewage basin, expect that solids and grease build up over time and the basin needs cleaning, which is a job for someone equipped for sewage, not a homeowner with a bucket. Check the check valve holds and the floats move freely without catching.
The battery on a backup pump is the quiet failure. A deep-cycle battery does not last forever and a dead battery is a backup that is not there, so it gets tested and replaced on a cycle. Hand the owner a short list with intervals and they keep the system alive. Hand them nothing and they find out it failed the same way everyone does, by stepping in it.
What to document
A pump system that nobody documented is a system the next person has to reverse-engineer in a flooded room. Record the selection and the settings so the pump can be matched, the floats can be reset, and the next tech knows what was actually installed instead of guessing from the pipe.
Capture the pump make, model, and type, whether it is sump, ejector, or grinder, the design flow in gpm and the total dynamic head it was selected against, the basin size, the float on and off levels and the drawdown, the discharge size, and the check, vent, and alarm details. Note the destination of the discharge and whether the AHJ approved it. If it is a duplex, record the alternator and the lag setup. The record is what lets someone size the replacement off the same curve instead of dropping in whatever fits the hole.
| Field to record | Why it matters |
|---|---|
| Pump make, model, and type | Lets the replacement match the curve and the service |
| Sump, ejector, or grinder | Wrong type is the most damaging substitution |
| Design GPM and TDH | The flow and head the pump was selected against |
| Basin size and drawdown | Sets the cycle and explains the float settings |
| Float on and off levels | Resetting floats without this is guesswork |
| Discharge size, check, vent | Confirms the install met the code minimums |
| High-water alarm and any duplex | Tells the next tech what protection exists |
| Discharge destination and AHJ sign-off | Proves the water and sewage went where allowed |
Common mistakes
- Putting a sump pump on a sewage load, where it clogs on the first solid it cannot pass.
- Leaving the sewage basin unsealed or unvented, so sewer gas comes up through the cover.
- Skipping the check valve, so the riser drains back and the pump short cycles on its own water.
- Setting the floats too tight or letting a tethered float catch the wall, which causes short cycling and stuck-float failures.
- Selecting the pump on horsepower instead of reading the curve at the actual GPM and total dynamic head, so it cannot make the head.
- Sizing only to flow and ignoring the friction and lift, then wondering why the basin backs up.
- Running no high-water alarm, so the first sign of a failed pump is water on the floor.
- Trapping or sagging the force main, which holds solids and air and chokes a pressurized line.
Field checklist
Want this checklist to run itself on every job — with photo proof and a signed record crews can hand the customer? That's FieldOS.
Standards and references
The framework lives in the adopted plumbing code, IPC or UPC, and the ejector and sump provisions are where the requirements sit, commonly Section 712 of the IPC and the equivalent ejector and sump section of the UPC. Those sections carry the solids-handling and discharge minimums, the 2 in solid for a pump receiving a water closet, the discharge size by building type, the sealed gas-tight cover, and the check valve and gate valve on the discharge. The basin vent runs off the venting chapter of the code, commonly Chapter 9 of the IPC. Section numbers shift between code cycles, so confirm them against the edition the jurisdiction has actually adopted and any local amendments before you cite them on a submittal.
The pump manufacturer's curve governs the selection. The code tells you the solids, the discharge size, the basin, and the venting; the curve tells you whether a given pump makes your gpm against your total dynamic head, and no code number substitutes for reading it. Size off the published curve for the pump you are actually installing, and follow the manufacturer's basin and float minimums.
Backwater and discharge-destination rules come from the same code and the local sewer authority. Where clear groundwater may go, whether the sanitary will accept it, the backwater valve requirements, and the connection of a force main to gravity are all set by the adopted code and the AHJ together. Confirm the discharge point and the backwater protection with the AHJ, because the local sewer rules and amendments are the ones that control the tie-in.
Units, terms, and conversions
The same pump shows up in a few unit systems across a curve, a spec, and a submittal, so the words have to line up.
Flow is gallons per minute, gpm, sometimes given in liters per second on imported pumps. Head is feet of head, the standard way pump curves and total dynamic head are stated, and it converts to pressure at roughly 2.31 ft of water per psi. Total dynamic head is the static lift plus the friction head, both in feet. A sewage ejector is sometimes called a sewage pump, distinct from a grinder pump that cuts solids and an effluent pump that handles septic-tank liquid with little solids. Drawdown is the working volume between the pump-on and pump-off float levels, and the force main is the pressurized discharge line carrying flow until it reaches gravity.
- TDH
- Total dynamic head, the static lift plus friction head the pump must overcome, in feet
- Static lift
- The vertical rise from the pump-off water level to the high point of the discharge
- GPM
- Gallons per minute, the flow the pump moves, read against head on the curve
- Drawdown
- The working volume between the pump-on and pump-off float levels that sets the cycle
- Force main
- The pressurized discharge line from the pump until it discharges into gravity flow
- Sewage ejector
- A solids-passing sewage pump, distinct from a grinder that cuts solids and an effluent pump that handles low-solids liquid
FAQ
What is the difference between a sump pump and a sewage ejector?
A sump pump moves only clear groundwater out of a sump pit and cannot pass solids. A sewage ejector lifts raw sewage with solids from below-grade fixtures into the gravity sewer and passes a 2 in solid. Put a sump pump on a sewage load and it clogs on the first solid.
How do you size a sewage ejector?
Total the drainage fixture units of the fixtures it serves, convert to a peak flow in gpm, and figure the total dynamic head as static lift plus friction in the discharge. Then pick the pump where your gpm and head cross on the manufacturer's curve, and confirm it passes the required solid size.
Does a sewage ejector basin need a vent?
Yes. A sewage ejector basin must have a sealed gas-tight cover and a vent to atmosphere, connected per the venting chapter of the adopted code. Without the vent the pump fights a pressure swing, the floats act up, and sewer gas finds its way into the building instead of out the vent.
Why does my pump short cycle?
Short cycling usually traces to a failed check valve letting the riser drain back, a basin too small for real drawdown, floats set too tight or stuck, or an oversized pump emptying the pit instantly. Fix the cause, set at least 6 in between the on and off points, before replacing the pump.
Can I use a sump pump for sewage?
No. A sump pump is built for clear water and cannot pass solids, so it clogs and fails on a sewage load. Below-grade fixtures with solids need a sewage ejector that passes a 2 in solid and discharges into a sealed, vented basin. Using a sump pump for sewage is a common and damaging mistake.
Do I need a check valve and a union on the discharge?
Yes. The code requires a check valve and a gate valve on a sewage pump discharge, with the check valve closest to the pump and the gate valve downstream. Add a union so the pump pulls without cutting pipe. Without the check valve the riser drains back and the pump short cycles.
Sewage ejector or grinder pump, which do I use?
Use a sewage ejector for below-grade fixtures dropping into a nearby gravity sewer or a septic tank, since it passes solids whole. Use a grinder to push sewage a long distance or high lift through small pressurized pipe into a force main. For a septic tank, use the ejector, not a grinder.
How big a solid does a sewage ejector pass?
A pump receiving a water closet must handle a 2 in spherical solid. The discharge minimum splits by building: a single dwelling commonly passes a 1 1/2 in solid with a 2 in discharge, while other buildings pass a full 2 in solid with a 3 in discharge. Confirm against the adopted code.
Do I need a high-water alarm on a sewage ejector?
On anything you care about, yes. A high-water alarm is a separate float above the pump-on level that warns you the pump failed, a float stuck, or the inflow beat the pump. Wire it to survive the pump's power loss. On critical sewage, run duplex pumps with an alternator so one failure does not flood the building.
How do I figure total dynamic head for a pump?
Add the static lift, the vertical rise from the pump-off level to the high point of the discharge, to the friction head, the loss through the pipe, fittings, and check valve at your design flow. That sum in feet is the head you carry to the pump curve at your gpm to select the pump.
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Codes cited in this guide
This guide is written and reviewed against the published standards below. Always confirm the current adopted edition with the authority having jurisdiction.